Travel Reference
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careful control for racial characteristics and lifestyle while comparing low- and high-alti-
tude populations.
Rarely, stroke has been reported in previously healthy sojourners at altitude and typic-
allyhasbeenascribedtodehydration,forcedinactivity,andpolycythemia.Strokemayalso
be a complication of highaltitude cerebral edema (HACE); clotting in cerebral blood ves-
sels is a common finding at autopsy.
Clinically, cerebral venous thrombosis (most strokes are arterial occlusions) is easily
confused with HACE. A number of reports emphasize the need for physicians to consider
this diagnosis in individuals with persistent neurologic symptoms after descent from alti-
tude.Inarecent seriesofindividuals eventually diagnosedwithcerebral venousthrombos-
is, all had recently been on long air flights and one had been mountaineering. An accom-
panying editorial suggested hypercoagulability or increased viscosity might be responsible
and emphasized that this condition is relatively easy to treat and must not be missed.
Whether acute high-altitude exposure contributes to a hypercoagulable state that predis-
posesindividuals tostrokes isasubject ofdebate. Theinteresting question ofwhether high
altitude might unmask cerebral arteriosclerosis and vascular insufficiency in asymptomatic
individuals has not been addressed.
Transient, focal neurologic abnormalities in the absence of HACE have been attributed
to transient ischemic attacks (TIAs). However, other possible etiologies include
cerebrovascularspasm(migraineequivalent),focaledema,andhypoxiainzonesofminim-
al cerebral blood flow. Most of these individuals have been young, healthy mountaineers,
not older individuals who would be expected to have arteriosclerotic vascular disease, the
usual cause of TIAs. One report described six cases of transient blindness that appeared
to result from a cerebral rather than an ocular process. Supplemental oxygen or carbon di-
oxide breathing promptly reversed the condition, which suggested vascular spasm rather
than occlusion. Descent provided slower relief. Others have described similar incidents as
well as other problems suggestive of TIAs. In all cases, recovery was complete, and the
fewindividualssubsequentlyevaluatedbyMRIhadnodetectableabnormalities.Theexact
etiology of these focal neurologic events remains a mystery and certainly warrants further
study.
Becausecerebralbloodvesselsdilateduringascenttoaltitude,personswithcerebrovas-
cular structural abnormalities, such as arteriovenous malformations or aneurysms, may be
at risk. Individuals with such abnormalities that have hemorrhaged have been encountered.
Persons with known cerebrovascular malformations should perhaps be advised to avoid
significant altitude exposure.
Brain Tumors
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